EP0102974A1

EP0102974A1 - Doppler radar area monitor

Info

Publication number: EP0102974A1
Application number: EP19830900786
Authority: EP
Inventors: Ian Simpson
Original assignee: Hoermann GmbH
Current assignee: Hoermann Warnsysteme GmbH
Priority date: 1982-03-12
Filing date: 1983-03-08
Publication date: 1984-03-21
Also published as: WO1983003308A1; DE3209093A1

Abstract

Dans un dispositif à radar Doppler pour la surveillance locale, l'oscillateur constitue en même temps le détecteur. Il contient un transistor à effet de champ, muni dans son circuit de source et de drain d'un élément de circuit pour le prélèvement des signaux de fréquence Doppler, connecté par l'intermédiaire d'un filtre. On obtient ainsi un dispositif particulièrement simple et de fabrication avantageuse, peu volumineux, léger et d'une fiabilité élevée.In a Doppler radar device for local surveillance, the oscillator simultaneously constitutes the detector. It contains a field effect transistor, provided in its source and drain circuit with a circuit element for the sampling of Doppler frequency signals, connected via a filter. This gives a particularly simple and advantageous manufacturing device, not bulky, light and of high reliability.

Description

Device for room surveillance using Doppler radar

The invention relates to a device for room surveillance by means of Doppler radar, containing a micro wave oscillator, a transceiver antenna and a detector for obtaining signals with Doppler frequency when moving within the monitored space.

A known device of this type ("Electronics Newspaper", Feb. 1980, p.8) contains a Gunn-Oszilla gate in cavity technology, a diode mixer as a detector and a planar transmit / receive antenna. A major disadvantage of this embodiment is that a significant proportion of the microwave power generated by the oscillator is consumed by the diode mixer when generating the Doppler-frequency useful signals. This results in a reduction in the efficiency of the room monitoring or the need to provide a correspondingly higher microwave power. Disadvantages are also the large space required by the cavity technology, the considerable weight and the considerable manufacturing costs.

The use of a Gunn diode as a mixer also belongs to the prior art. The Gunn diode is arranged in a cavity that is connected to the antenna. Doppler-frequency signals that are injected into the cavity cause a current change in the Gunn diode caused by a low frequency circuit is evaluated. The main disadvantage of this known embodiment is that the mixing effect achieved with the Gunn diode is very small, so that a high interference component results when amplified. Such a device for room surveillance therefore has only a relatively short range.

The invention is therefore based on the object, while avoiding these deficiencies of the known designs, to provide a device for space monitoring by means of Doppler radar, which is distinguished by a particularly simple, cost-saving production, a small space requirement and a low weight and which is very reliable in relation to environmental influences insensitive mode of operation.

This object is achieved in that the detector is formed by the oscillator which also acts as a mixer and which contains a field effect transistor (FET), in the source-drain circuit of which a circuit element connected via a filter is provided for tapping the Doppler-frequency signals.

Circuits with FET have previously been used as mixers. However, a separate oscillator has always been provided for these designs seen for other applications. Although these known circuits have excellent mixing efficiency, they are nevertheless unsuitable for devices for room surveillance because of their use separate FET for oscillator and detector represents a prohibitively large expense for room monitoring devices.

The invention is based on the knowledge that it is possible, taking into account the conditions given in a room monitoring using Doppler radar, to design the oscillator provided with a FET at the same time as a detector (mixer) and the Doppler frequencies obtained by the detector

Tapping signals from a circuit element which is connected to the source-drain current circuit of the FET via a filter.

This results in a particularly simple circuit which can be produced in a cost-saving manner with a small space requirement and a small weight and which has a very reliable mode of operation which is insensitive to external disturbances.

Further details of the invention are the subject of the dependent claims and are explained in connection with the description of some exemplary embodiments.

1 shows a schematic representation of the device for room surveillance according to the invention. It contains an oscillator 1, which is supplied by a DC voltage source 3 via a resistor 2. The oscillator 1 is connected to an antenna 5 via a connection circuit 4. The microwaves generated by the oscillator 1 are emitted by the antenna 5 into the room to be monitored. The reflected signals are picked up again by the antenna 5 and fed to the oscillator 1, which is also designed as a detector. A movement in the monitored room results in a frequency difference (Doppler frequency shift) between the emitted and the received microwaves. These Doppler-frequency signals - as will be explained in more detail with the aid of some exemplary embodiments - generate a corresponding voltage change at the resistor 2, which can be tapped off at the terminals 6, 7 of this resistor 2 and processed further by a suitable low-frequency circuit.

A first embodiment of the oscillator, which is also designed as a detector (mixer), is illustrated in FIG.

The oscillator contains a GaAs FET 8, the source, drain and gate connections of which are denoted by s, d and g, respectively. Source and gate connections s, g of FET 8 are coupled via a first impedance 9. The

Source terminal s is connected via a first inductor 10 and a first resistor 11 to a bias voltage source (terminal 12). The Doppler-frequency signals are tapped at the terminals 13, 14 of the resistor 11.

The drain terminal d of the FET 8 is via a first

Capacitance 15 is connected to the antenna (connection 16) and is connected in series via a second inductor vity 17 and a second resistor 18 connected to ground. The connection point between the first resistor 11 and the first inductor 10 is connected to ground via a second capacitance 19. The gate connection g of the FET 8 is connected to ground via the parallel connection of a third resistor 20 and a third inductor 21.

The mode of operation of the circuit according to FIG. 2 is as follows:

The FET 8 is fed from the terminal 12 via the resistor 50. If you first think of impedance 9, i.e. the feedback between the source and gate connection, then a certain quiescent current is established. The impedance 9 acting as feedback, which is formed, for example, by a dielectric resonator, results in a resonance gain of a certain frequency of the current flowing in the source-drain circuit. The feedback from the source to the gate connection of the FET 8, which acts with a phase shift of 180 °, results in a stable oscillation at a frequency which corresponds to the natural frequency of the dielectric resonator, i.e. corresponds to the impedance 9.

The current flowing in the source-drain circuit generates a sinusoidal voltage at the series connection of the inductor 17 and the resistor 18. The inductance 17 represents a large one for this current

Impedance, so that there is a high output voltage, the capacitance 15 (that for the Oszilla gate frequency represents a low impedance)

Port 16 is transmitted.

Self-excitation of the FET 8 is prevented by the resistor 20 and the inductance 21. The inductor 10 and the capacitor 19 form a low pass filter. Resistor 18 provides sufficient positive bias of the drain terminal against the gate terminal.

The function of the circuit according to FIG. 2 as a detector (mixer) for obtaining the Doppler-frequency signals at resistor 11 is as follows:

As already mentioned in the explanation of the oscillator function, a sinusoidal voltage of the oscillator frequency occurs at the series connection of the inductor 17 and the resistor 18. If the transmit / receive antenna connected to the connection 16 now receives microwaves with a frequency that is slightly different from the transmitted frequency (due to movement in the monitored space), the following sum voltage v results at the drain connection d of the FET 8:

(1) V = V ₁ sin ω ₁ t + V ₂ sin ω ₂ t

Here is

V ₁ = the peak value of the voltage of oscillation frequency ω ₁

V ₂ = the peak value of the voltage with a frequency ω ₂ shifted by the Doppler frequency. The second expression in equation (1) results in a change in the current flowing through the FET 8. The following relationship applies to the current i in the source-drain channel of the FET 8:

Here mean idss = saturation current for a certain voltage

V _gd = voltage between gate and drain connection Vp = so-called pinch-off voltage of the FET.

If you insert (1) in (2), you get for the current i

By transforming (3) one obtains

Expression A is time independent and results in a small change in quiescent current through the FET. The expression B depends on the frequency difference ω ₁ - ω ₂ ; this expression B thus depends on the Doppler frequency (ω ₁ - ω ₂ ) caused by a movement in the monitored space.

The expression C consists of two summands, which depend on the transmitted and on the received frequency (ω ₁ and ω ₂ ). Expression D contains three

Summands, the first two of the second

Harmonics of the frequencies ω ₁ or Co depend, while the third summand depends on the sum frequency

(ω ₁ + ω ₂ ) depends.

It can thus be seen that the introduction of a second

Signals at the drain of the FET a series of

Expresses effects. This is based on the non-linear

Current-voltage characteristic of the FET and can be used for a mixed function, in particular for determining the Doppler frequency shift.

In the case of room monitoring using Doppler radar, the shifted frequency ω _{2 is} very close to the oscillator frequency ω ₁ . The difference ω ₁ - ω ₂ is therefore very small and is of the order of magnitude of a few Hz. This low-frequency voltage can easily be tapped at the resistor 11 (FIG. 2). In contrast, the signals according to the expressions C and D are very high frequencies, which are blocked by the low-pass filter formed by the inductor 10 and the capacitor 19, and therefore no voltage can produce at the resistor 11. The signal according to

Expression A is frequency independent; it only affects the no-load voltage across resistor 11 and therefore does not interfere with the extraction of the Doppler-frequency signals.

As explained above, the signal V ₂ sinω ₂ t occurring at the drain connection of the FET in addition to the oscillator oscillation results in different mixed products from which the Doppler-frequency signal can be taken. The influence of the signal V ₂ sin ω ₂ t on the oscillator function is extremely small, as the following consideration of the relative values shows;

For a typical Doppler sensor, assume:

V ₁ = 0.7 sin ω ₁ t V ₂ = 0.07 sinω ₂ t

Vp = 5 volts

B = - 0.05cos (ω ₁ -ω ₂ ) t

C = - 7sin ω ₁ t - 0.7sinω ₂ t

The largest expression here is A; however, this is a DC component and therefore has no influence on the oscillator function. The next largest expression is C, the expression with the frequency ω ₁ dominating. However, this is precisely the component that maintains the vibration. As a result, if there are no other frequency components of comparable size, the oscillator function remains practically unaffected by the presence of the much smaller signal with the frequency ω ₂ .

A further exemplary embodiment of the oscillator designed according to the invention as a detector (mixer) is shown in FIG.

The source terminal s of the FET 22 is connected to ground. The drain and gate terminals d and g of the FET 22 are coupled via a first capacitance 23. The gate connection g is also connected to ground via a first impedance 24 and the series circuit of a first inductance 25 and a second capacitance 26 arranged in parallel therewith. A first bias source (terminal 27) is connected between the inductor 25 and the capacitor 26.

The drain terminal d of the FET 22 is connected to the antenna (terminal 30) via a second impedance 28 and a third capacitance 29. The connection point between the impedance 28 and the capacitance 29 is connected to ground via the series connection of a second inductance 31 and a fourth capacitance 32. A second bias voltage source (connection 34) is connected to the connection point between the inductance 31 and the capacitance 32 via a resistor 33. The Doppler-frequency signals are tapped at the terminals 35, 36 of the resistor 33.

The capacitance 23 here represents the feedback from the drain to the gate connection of the FET 22. The oscillator gate frequency is determined by the impedance 24, which is matched to the FET 22. The impedance 28 (for example a dielectric resonator) serves to stabilize the oscillator function. In the ductivities 25, 31 and the capacities 26, 32 represent low-pass filters in the bias circuits. The capacitance 29 represents a low impedance for the oscillator frequency, but keeps the voltage from the output terminal 30 off.

In the further exemplary embodiment shown in FIG. 4, the gate connection g of the FET 37 is connected to ground via a first inductance 38. The source connection s of the FET 37 is connected to ground via a first impedance 39 and a series circuit of a second inductor 40 and a first capacitance 41 arranged in parallel therewith. A first bias voltage source (connection 42) is connected to the connecting point of the inductance 40 and the capacitance 41

The drain connection d of the FET 37 is connected to the antenna via a second capacitance 43 (connection 44) and is connected to ground via the series connection of a third inductance 45 and a third capacitance 46. At the connection point of the inductance 45 and the capacitance 46 is a second bias voltage source (connection 47) via a counter was connected 48, at whose terminals 49, 50 the Doppler-frequency signals are tapped.

The inductance 38 effects the feedback between the source and gate connection of the FET 37. The frequency of the oscillator is determined by the impedance 39; it can be formed by a partial length of the transmission line, a dielectric resonator or a cavity. Inductors 40, 45 and capacitors 41, 46 form a low-pass filter in the bias circuits. The capacitance 43 represents a low impedance for the oscillator frequency, but keeps the bias voltage away from the antenna output.

In the further exemplary embodiment shown in FIG. 5, the drain and source connection d, s of the FET 51 are coupled via a first capacitance 52. The drain terminal d is connected to ground via a first impedance 53. The gate connection g is connected to ground via a first inductance 54.

The source connection s of the FET 51 is connected to the antenna (connection 56) via a second impedance 55 and connected to ground via the series connection of a second inductance 57 and a second capacitance 58. A bias voltage source (connection 59) is connected to the connection point of the inductance 57 and the capacitance 58 via a resistor 60, from which the Doppler-frequency signals are tapped. 6 shows an embodiment which largely corresponds to the arrangement according to FIG. For the same construction parts, the same reference numerals are used accordingly. In contrast to FIG. 2, in the embodiment according to FIG. 6, the circuit element located in the source-drain circuit of the FET 8, on which the Doppler-frequency signals are tapped, is formed by a constant current source 90.

The operation of this circuit is as follows. When switched on, the constant current source 90 delivers a predetermined current into the source-drain circuit FET 8; the current value depends on the preload. The voltage occurring between the terminals 13, 14 then depends on the resistance of the source-drain path. Movements in the monitored room then - as already explained - result in current fluctuations (with Doppler frequency) of the low-frequency components, which lead to corresponding voltage fluctuations between terminals 13, 14. The filter formed by the inductor 10 and the capacitor 19 has the same function as described in FIG. 2; it keeps high-frequency signals away from the bias circuits.

The oscillator according to the invention, for which some exemplary embodiments have been explained with reference to FIGS. 1 to 6, can expediently be designed in a microstrip design (microstrip or stripline). To explain what is to be understood here under "microstrip construction", reference is first made to FIGS. 7 and 8.

Fig. 7 shows the construction, which is called "stripline construction" in the Anglo-American literature. In this construction suitable for microwave technology, two flat insulating plates 61, 62 are provided, which have a metallic layer 61a or 62a on their outside, which is usually at ground potential. A conductor 63 in the form of a thin metal strip is sandwiched between the insulating plates 61, 62 and serves as a microwave line.

In contrast, FIG. 8 shows the so-called “microstrip construction”. Only one insulating plate 64 is provided here, which is provided on one side with a metallic layer 64a, which is usually held at ground potential, and on the other side, the conductor 65 intended for conducting the microwaves wearing.

In the present context, the term "microstrip design" is understood to mean both the designs shown in FIGS. 7 and 8.

According to an expedient embodiment of the invention, the antenna in microstrip design (as Planar antenna). An embodiment example in which the oscillator, antenna and their connecting lines are formed in microstrip design and are arranged on the same carrier material is shown in FIGS. 9 and 10. 9 shows the oscillator and FIG. 10 shows the antenna arranged on the same carrier material (thus adjoining to the right of FIG. 8).

The oscillator according to FIG. 9 is constructed in accordance with the circuit according to FIG. 2. The same reference numerals are accordingly provided for the individual parts as in FIG.

On the carrier plate made of insulating material

66, the FET 8 is arranged in a microstrip design. The gate, drain and source connections of the FET 8 are connected to corresponding connection conductors, which are designated as 67, 68, 69 and 70. Between the connection conductors 67 and 69, the impedance 9, a dielectric resonator, is provided as a feedback between the source and gate connection. Otherwise, the details of the circuit result from the explanation of FIG. 2. The ground metallization of the carrier plate 6 is denoted by 71.

10 shows the antenna 72 belonging to the oscillator according to FIG. 9. It is arranged on the same carrier plate 66 as the oscillator and is connected to it via the connection 16. The antenna designed in microstrip design contains several antennas in the illustrated embodiment elements 73 to 77, each consisting of strip-like conductors pointing in the opposite direction and fed by the common connection 16 with microwave energy.

Numerous other designs of planar antennas are of course also possible within the scope of the invention. For example, the strips of the individual antenna elements can be offset from one another by 90 ° in order to achieve a circular polarization of the antenna beam.

FIG. 11 shows an exemplary embodiment in which a horn antenna 78 is combined with an oscillator 79 which is designed in a microstrip design and projects into the horn antenna 78 with a conductor strip 80. The microwaves generated by the oscillator are transmitted through the conductor strip 80 into the horn antenna 78 and radiated by the latter. As in the exemplary embodiments explained, the microwaves picked up by the antenna are fed to the oscillator, which is designed as a detector (mixer), and generate the Doppler-frequency useful signals.

In the likewise only very schematically illustrated exemplary embodiment according to FIG. 12, an assembly 81 which contains the oscillator with FET is connected to a horn antenna 83 via a coaxial connection 82. Instead of a horn antenna, an antenna in microstrip design or any other antenna with coaxial flange can of course also be used here. Finally, FIG. 13 illustrates an exemplary embodiment in which an FET 51 is provided in the interior of a cavity resonator 85 connected to a horn antenna 84 and is arranged in a so-called coaxial packing on a support 87. The power supply of the FET 51 takes place via a connection 88 which is passed through the wall of the cavity resonator 85 in an insulated manner.

In the exemplary embodiment according to FIG. 13, the

Circuit selected according to Fig.5. The gate connection g of the FET 51 is accordingly connected via an inductance 54 (which is formed by a short wire) to the wall of the cavity resonator 85 which is at ground potential. The support 87 forms the Im pedanz 53 according to Fig.5. The dimensions of the support 87, the connection 88 and the inductor 54 are chosen so that there is an oscillation with the resonance frequency of the cavity (determined by the internal dimensions of the cavity resonator 85 and horn antenna 84).

The capacitance 52 (FIG. 5), which forms the feedback from the source to the drain connection of the FET 51, is determined by the distance between the support 87 and the connection

88 determined. The impedance 55 is formed by the cavity resonator 85. This impedance stabilizes the oscillation and transmits the power to the horn antenna 84. The inductance 57 and the capacitance 58 (see FIG. 5) are formed by the connection 88. The Doppler frequency useful signal is taken from the resistor 60. The function also corresponds here the example explained in detail with reference to FIG. 2.

In conclusion, it should also be pointed out that the source and drain connections can in principle be interchanged with most low-power field-effect transistors.

It should also be noted that pulse operation is also possible. In this case, the low-pass filter provided in the described exemplary embodiments is replaced by a band filter, the pass band being below the oscillator frequency of the FET.

Claims

Claims:

1. Device for room monitoring by means of Doppler radar, containing a microwave oscillator, a transmit / receive antenna and a detector for obtaining signals with Doppler frequency when moving within the monitored room, characterized in that the detector is also used as a mixer acting oscillator is formed, the one

Contains field effect transistor (FET), in the source-drain circuit of which a circuit element connected via a filter is provided to handle the Doppler-frequency signals.

2. Device according to claim 1, characterized by a GaAs FET.

3. Device according to claim 1, characterized in that the oscillator in microstrip design

(microstrip or stripline) is formed.

4. The device according to claim 1, characterized in that the antenna is designed as a planar antenna in micro stripe design.

5. Device according to claims 3 and 4, characterized in that the oscillator, antenna and their connecting lines are formed in microstrip design and are arranged on the same carrier material.

6. The device according to claim 1, characterized in that the antenna is designed as a horn antenna and is connected to the oscillator via connecting lines in microstrip design or in coaxial design.

7. The device according to claim 1, characterized in that the oscillator is arranged in a coaxial design in a cavity antenna connected to a horn antenna.

8. The device according to claim 1, characterized by the following circuit of the oscillator:

a) source and gate of the FET (8) are coupled via a first impedance (9);

b) the source connection is connected via a first inductance (10) and a first resistor (11), at which the Doppler-frequency signals are tapped, to a bias voltage source (connection 12);

c) the drain connection of the FET is connected via a first capacitance (15) to the antenna (connection 16) and via the series circuit of a second inductance (17) and a second resistor (18) to ground;

d) the connection point between the first opponent (11) and the first inductor (10) is connected to ground via a second capacitance (19); e) the gate connection of the FET is connected via the parallel circuit of a third resistor (20) and a third inductor (21) to ground.

9. The device according to claim 1, characterized by the following circuit of the oscillator:

a) The source connection of the FET (22) is connected to ground;

b) drain and gate connection of the FET are coupled via a first capacitance (23);

c) the gate connection is via a first impedance

(24) and the series circuit connected in parallel to this, a first inductor (25) and a second capacitance (26) connected to ground;

d) between the first inductance (25) and the two-th capacitance (26), a first bias voltage source (terminal 27) is connected;

e) the drain connection is connected to the antenna (connection 30) via a second impedance (28) and a third capacitance (29);

f) the connection point between the second impedance (28) and the third capacitance (29) is via the series connection of a second inductance

(31) and a fourth capacitance (32) connected to ground; g) at the connection point between the second inductance (31) and the fourth capacitance (32) is connected via a resistor (33), the Doppler-frequency signals are tapped, a second bias voltage source (connection 34) to.

10. The device according to claim 1, characterized by the following circuit of the oscillator:

a) The gate connection of the FET (37) is connected to ground via a first inductance (38);

b) the source connection is connected to ground via a first impedance (39) and a series circuit arranged in parallel therewith of a second inductance (40) and a first capacitance (41);

c) a first bias voltage source (terminal 42) is connected to the connection point of the first capacitance (41) and the second inductance (40);

d) the drain connection is connected via a second capacitance (43) to the antenna (connection 44) and is connected to ground via the series connection of a third inductance (45) and a third capacitance (46);

e) to the connection point of the third inductance (45) and the third capacitance (46) is a second bias voltage source (terminal 47) a resistor (48) is connected to which the Doppler-frequency signals are tapped.

11. The device according to claim 1, characterized by the following circuit of the oscillator:

a) drain and source connection of the FET (51) are coupled via a first capacitance (52);

b) the drain connection is connected via a first impedance (53) to ground;

c) the gate connection is connected to ground via a first inductance (54);

d) the source connection is connected via a second impedance (55) to the antenna (connection 56) and via the series circuit of a second inductance (57) and a second capacitance (58) to ground;

e) at the connection point of the second inductance (57) and the second capacitance (58), a bias voltage source (connection 59) is connected via a resistor (60), at which the Doppler-frequency signals are tapped.

12. The apparatus according to claim 1, characterized in that in the source-drain circuit

FET (8) a constant current source (90) is arranged, at the terminals (13, 14) of which the Doppler-frequency signals can be tapped.